Before a communication protocol of controller area network (CAN) bus interface is developed, the electric components in the vehicle electrical system mostly communicated with each other by a point-to-point manner for data transmission and commanding. The communication protocol of CAN bus interface can integrate sensors and the controller of the vehicle electrical system by a simple serial bus. Thus, CAN bus interface now is a widely used communication interface in the vehicle electrical system, and it can be further used in the field of industrial control, medical instrument and the automatic control.
Specified by the communication protocol of CAN bus interface, all nodes of the system are linked to a data bus for data transmission and control. Furthermore, the data to be transmitted is packaged into a data packet and the data packet is converted to a differential signal so as to transmit the data to the data bus for achieving the data transmission. The communication protocol of CAN bus interface further specifies several kinds of error frames, such as cyclic redundancy check (CRC) error frame, acknowledge error frame, form error frame, stuff error frame and bit error frame.
The communication protocol of CAN bus interface further specifies the error mechanism, such as error active mechanism, error passive mechanism and bus off mechanism. The counters for respectively accumulating transmitting and receiving errors are used, and when the counting value of the transmitting or receiving error is less than 127, the corresponding node operates in the error active mechanism. In the error active mechanism, when the error occurs for one data packet, the operation for the data packet being transmitted is interrupted, and the corresponding counting value is accumulated. Then, the bus resumes in the normal status, and the data packet is retransmitted.
When the counting value of the transmitting or receiving errors is larger than 127, the corresponding node operates in the error passive mechanism. The error frame can be still transmitted, the corresponding counting value is still accumulated, but the operation of the data packet being transmitted is not interrupted. Then, after the error frame has been transmitted successfully, the corresponding node waits for a time period to retransmit the data packet.
If the counting value of the transmitting or receiving errors is larger than 255 unfortunately, the corresponding node operates in the bus off mechanism. In the bus off mechanism, the corresponding node equivalently operates in the bypass status and is unable to receive and transmit any data packet. The corresponding node must be reset to return the error active mechanism.
In short, CAN bus interface has the robust communication protocol for solving data collision and arbitration, and also has the function for monitoring the status of the bus. However, when burst noise occurs, the bus is still unstable. Even when the node fails, the communication protocol of CAN bus interface merely accumulates the errors through the error frame. Then, when the counting value of the accumulated errors is larger than a predetermined value, the corresponding node is forcedly separated from the bus (i.e. bus off mechanism). The error data packets are prevented from occupying the bus long, but the abnormality of the corresponding node is still not solved.
Accordingly, due to lack of the link reestablishment mechanism, CAN bus interface is not suitable for the application of the battery system with the hierarchical energy management function. When the controller (i.e. master node) cannot obtain the battery information of the battery set (i.e. slave node) several times, the battery set is separated from the bus forcedly. If the battery set is not reset manually, the stability of the supplied electricity will be affected.